John,
My chemistry is pathetic but I do appreciate the practical advice ;-)
Rick
-----Original Message-----
From:
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com]
On Behalf Of smilingcat90254
Sent: Friday, November 23, 2012 11:12 AM
To:
Homebrew_PCBs@yahoogroups.comSubject: [Homebrew_PCBs] Re: Ratio of Ferric Chloride to copper?
me bad yes you are right. It's atomic weight one should be using. This is
what happens late at night. :embarassed:
The reaction as I understand it is two fold.
FeCl3 + Cu --> FeCl2 + CuCl
then FeCl3 + CuCl --> FeCl2 + CuCl2
so the end game you get is 2FeCl3 + Cu --> 2FeCl2 + CuCl2
using correct atomic weight we need 324g of FeCl3 to etch away 63.5g of
copper.
not sure how copper chloride can continue to react with copper... maybe it
has to do with Keq value. Partial dissociation and if you have excess [Cl]
then I could see that the solution is trying to get to the equilibrium of
[Cu++], [Cu+]...
Pchem and statistical thermodynamics in college was oh so many years ago.
Too long ago. I ended up being an electrical engineer instead. :embarassed:
went from Applied physics (then two mile id happened) changed to chem e
(then Bopal India with Union Carbide happened) so ended up as electrical
engineer. wink wink :D
--- In Homebrew_PCBs@yahoogroups.com, "John Anhalt" <janhalt@...> wrote:
>
> First off, you seem to have confused atomic number, which is the number of
protons in the atom, with atomic weight. The atomic weight of copper is
63.5 and the atomic weight of FeCl3 is 162 (molecules have no atomic
number).
>
> More important, you need to define the equation, You seem to be using
this equation:
>
> 2FeCl3 + Cu ===> 2FeCl2 + CuCl2
>
> Certainly, that is one appropriate equation. But are there others? How
can you explain that CuCl2 itself can be used to etch copper? Is it
possible that some of the ferrous (II) chloride could be converted to an
iron oxide, thus leaving more chloride to form copper chloride? Or,
perhaps, the copper chloride converts to copper (II) oxide, which also
releases chloride? Also, remember that copper has two oxidation states
that, so Cu2O and CuO are both possible. When doing etching, particularly
if there is excess HCl, several reactions are occurring.
>
> Simply, the chemistry involves oxidation, so oxygen in the solution can
also play a part, and in the presence of excess HCl, oxygen can play a large
part.
>
> The article by Adam Seychell has been referenced here before times and is
posted on the site. He explains how CuCl2 can be used as an etchant and be
continuously regenerated by bubbling air through the solution with
occasional addition of HCl.
>
> Finally, when people refer to ferric chloride as an acid, remember there
are different definitions for acids. When dissolved in water, ferric
chloride produces and acidic solution.
>
> As for the original question, don't worry about the ratio of ferric
chloride to copper. Some people actually just sponge it on and get quite
rapid etching. The advantage of sponging is that exposure to oxygen is
maximized. Others spray the ferric chloride, which is also a rapid method.
Another method is to put both the PCB and ferric chloride in a plastic bag
and squish it around. If you use a bath to immerse the PCB for etching,
remember that the concentration of ferric chloride in the bath will be about
40%. If you have 1 oz copper clad for your PCB, that is 1 oz of copper per
square foot. Only some of that is removed. So, it is unlikely you could
ever run into a situation of having too little ferric chloride assuming you
have sufficient liquid present to cover the board.
>
> John
>
> ----- Original Message -----
> From: smilingcat90254
> To: Homebrew_PCBs@yahoogroups.com
> Sent: Thursday, November 22, 2012 9:51 PM
> Subject: [Homebrew_PCBs] Re: Ratio of Ferric Chloride to copper?
>
>
>
> hmmm... can't really go by volume of FeCl3 (Ferric chloride) and volume
of copper. Wht you need to know is how many moles of each (chemists way of
counting number of atoms or molecules) will react together. read about
atomic weight, Copper weighs 29gram/mole whereas FeCl3 weighs 77g/mole.
>
> And now you want to know how much ferric chloride can "eat" copper.
> It takes two molecules of ferric chloride to "eat" one atom of copper
and turn it into one molecule of Copper chloride (CuCl2). I think it was...
>
> So you need 154g of ferric chloride to etch 29g of copper.
>
> You have to know the concentration of your ferric chloride solution.
>
> BTW, ferric chloride isn't an acid, its a salt like sodium chloride
(table salt).
>
> hope this answers your question.
>
> --- In Homebrew_PCBs@yahoogroups.com, "RickS" <rgsparber@> wrote:
> >
> > Does anyone know the ratio of needed Ferric Chloride by volume to the
volume of copper being removed? I am assuming 110F for the acid and constant
agitation.
> >
> > Thanks in advance,
> >
> > Rick Sparber
> >
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
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